All these tips are exceedingly valid, but has something been missed?
The 172 had an expected (even better than that) burn for the first 90 minutes of flight. Other than an actual, serious fuel leak, or a seriously distorted bladder tank ex AAA (AND BBB), what could have changed during the second sector to cause such a discrepancy in expected vs actual burn?
speed2height dipped the tanks 3/4 full ex BBB...